| 1. |
- Bergström, Gunnar, et al.
(författare)
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Durability testing for 100 year lifetime for buried non-pressure plastic pipes
- 2006
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Ingår i: Plastics Pipes XIII.
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Konferensbidrag (refereegranskat)abstract
- For plastics pipes used for underground drainage and sewerage there is at present no internationally accepted method for the evaluation of durability. This makes it difficult to make an objective assessment for both new materials and new pipe designs entering the market. This paper presents a possible future structure of such a durability evaluation for nonpressure pipes. Based on an experimental study of pipes made from a filled and an unfilled PP material and one made from an HDPE material different damage mechanisms and changes in pipe characteristics were observed when the pipes were exposed to long-term deflection and long term (one-year) ageing at +95 °C. A CAED methodology is also described which was used to investigate the distribution and time dependence of pipe stresses.
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| 2. |
- Forsaeus Nilsson, Stefan, 1972, et al.
(författare)
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Brittle fracture in casing pipes
- 2006
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Ingår i: 10th International Symposium on District Heating and Cooling.
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Konferensbidrag (refereegranskat)
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| 3. |
- Forsaeus Nilsson, Stefan, 1972, et al.
(författare)
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Damage to coated plastics pipes from trenchless laying techniques
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This project aims at evaluating an external coating on plastics pipes; and its protective function against scratches and scoring damage from trenchless laying techniques. PE100 pressure pipes with four different coatings were tested in horizontal drilling and pipe bursting field trials. During the tests, the lengthwise and cross-sectional deformations of the pipe were measured along with the traction force. The pipes’ surfaces were examined with respect to scratches, and the depth of the most prominent ones were determined. Of the two laying techniques, pipe bursting was the one that caused the deepest scratches. Horizontal drilling was not significantly worse than ordinary handling during transport and preparation with respect to scratch depth. Dragging of the pipe above ground on asphalt surfaces caused severe damage to the pipe wall. The deepest scratches were seen on two pipe selections with soft coatings. Due to their thickness, however, these coatings were not penetrated and thus successfully protected the main pipe wall. The hardest coating tested, made of polypropylene, was also the thinnest one, and it was penetrated at one location during the pipe bursting test. The traction force on the pipe was significantly higher during horizontal drilling than during pipe bursting. On the other hand, ovalisation of the pipe’s cross-section was greater during pipe bursting.
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| 4. |
- Forsaeus Nilsson, Stefan, 1972, et al.
(författare)
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Skador på skyddsmantlade plaströr vid grävningsfri förläggning
- 2005
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This project aims at evaluating an external coating on plastics pipes, and its protective function against scratches and scoring damage from trenchless laying techniques. PE100 pressure pipes with four different coatings were tested in horizontal drilling and pipe bursting field-trials. During the tests, the lengthwise and cross-sectional deformations of the pipe were measured along with the traction force. The pipes’ surfaces were examined with respect to scratches, and the depth of the most prominent ones were determined. Of the two laying techniques, pipe bursting was the one causing the deepest scratches. Horizontal drilling was not significantly worse than ordinary handling during transport and preparation with respect to scratch depth. Dragging of the pipe above ground on asphalt surfaces caused severe damage to the pipe wall. The deepest scratches were seen on two pipe alternatives with soft coatings. Due to thic kness, however, these coatings were not penetrated and thus successfully protected the main pipe wall. The hardest coating tested, a polypropylene alternative, were also the thinnest one, and was penetrated at one location during the pipe bursting test. The traction force on the pipe was significantly higher during horizontal drilling than during pipe bursting. On the other hand, ovalisation of the pipe’s cross-section was greater during pipe bursting.
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| 5. |
- Forsaeus Nilsson, Stefan, 1972, et al.
(författare)
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Spröda brott i mantelrör
- 2005
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Vid ett flertal tillfällen har Rapid Crack Propagation (RCP) inträffat i mantelröret hos stora fjärrvärmerör. RCP är ett mycket snabbt sprickförlopp där sprickan drivs fram av ringdragspänningar i mantelröret. Det är ett problem framför allt vid arbete på rören i låga temperaturer. Dels blir mantelrörsmaterialet sprödare då det kyls ned, och dels gör en temperatursänkning att ringdragspänningar byggs in i mantelröret då det förhindras att dra ihop sig av stålrör och PUR-skum. RCP-sprickor i fjärrvärmemantelrör har dokumenterats vid temperaturer kring –18 °C men sannolikt har fenomenet inträffat i enstaka fall redan vid några grader under noll. Tre olika polyetenmaterial utvärderades med avseende på risken för spröda brott i mantelrör. Dels ett unimodalt material av PE80-kvalitet som har använts i stor utsträckning tidigare, dels ett modernare unimodalt PE80-material som används emellanåt idag och slutligen ett bimodalt PE80-material av en kvalitet som för närvarande används av de flesta tillverkare. Generellt sett är modernare material avsevärt tåligare med avseende på spröda brott då det är en viktig utvecklingsparameter hos råmaterialtillverkarna. Provningar genomfördes på polyetenrör av både stor (upp till 630 mm diameter) och liten (160 mm) dimension. Ett hanteringsprov genomfördes där rören kyldes ned och bearbetades med elverktyg på samma sätt som sker i fält. Här uppstod ett RCP-brott vid –25 °C under skärarbete med vinkelslip på ett rör med diameter 500 mm av det modernare unimodala PE80 materialet. Samma material sprack även vid slagprovning enligt SS-EN 253 vid –20 °C på såväl liten som stor dimension. Den bimodala polyetenvarianten klarade båda provningarna utan brott. En serie slagprov genomfördes på rör med diameter 160 mm med en egenutvecklad provningsmetodik med avsikten att ringa in kritiska temperaturer och temperaturspänningsnivåer vid vilka man bör iaktta särskild försiktighet. Resultaten visar att det bimodala polyetenmaterial som provats är så tåligt med avseende på spröda brott att det knappast är förknippat med någon större risk att hantera dem i normalt vinterklimat. Det äldre materialet, som sprack vid hanteringsprov och slagprov enligt SS-EN 253, är dock betydligt känsligare och en spänningsanalys visar att det, för stora dimensioner, finns en påtaglig risk för sprödbrott redan vid temperaturer några grader under noll. Slagsegheten hos de olika materialen har också utvärderats med sk Charpyslagprovning, som provningsmässigt är betydligt enklare att genomföra än slagprov i fullskala på hela rör. Även här var syftet att bestämma en kritisk omslagstemperatur mellan segt och sprött beteende. Tydliga skillnader kunde ses mellan de olika polyetenkvaliteterna. Sannolikt finns en korrelation mellan resultaten från Charpyprov och rörslagprov. Emellertid saknas statistiskt underlag för att dra några kvantitativa slutsatser, men med mer underlag skulle metoden troligtvis kunna användas för klassificering och kravgränser.
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| 6. |
- Thörnblom, Kristian, 1976, et al.
(författare)
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Durability of non-pressure polypropylene pipes
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- For plastics pipes used for underground drainage and sewerage as well as for other nonpressure pipe applications there are at present no internationally accepted methods for the evaluation of the durability of the material. In practice pipe material selection is based upon comparative operational experience of the different materials over a number of years. This means that there are no objective means of assessing new pipe designs and new pipe materials coming onto the market. Reasonably there will be a spread in material qualities with some materials having good properties and some being of lower quality (e.g.recycled materials or materials with very high filler content). Without a recognised testing method it is not possible to rank these alternatives or restrict their use to specific application areas without awaiting the outcome from their use in the field. It is today an established fact that plastics pipes are well suited for underground water and sewer systems due primarily to their flexibility to soil movement and their corrosion resistance. Pipe deflections of up to 10% of the diameter has been shown to be no problem for plastics pipes according to extensive field studies performed by the Teppfa organisation. However, it is also a fact, not so well known, that the stresses in the pipe wall can still be at a relatively high level after 10 or 50 years of use under such conditions. With new pipe structures and possibly lower quality pipe materials, the stresses and strains in the pipe may well exceed the limiting properties of the material and thereby put the reliable function of the pipe system at risk. One main objective of this study has been to look for limiting values of strain for the different materials, above which excessive deformation or failure can occur. The evaluation method presented is based on the use of a range of durability test methods on mainly polypropylene but also on one polyethylene material. The important characteristics studied include the stress relaxation/strainability properties, slow crack growth / notch resistance, thermo-oxidative degradation and environmental stress cracking. The basic properties of the materials are developed by tests on solid wall pipes. The relaxation behaviour of the materials was also modelled and compared using CAED methodology.
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| 7. |
- Thörnblom, Kristian, 1976, et al.
(författare)
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The extractability of phenolic antioxidants into water and organic solvents from polyethylene pipe materials - Part I
- 2011
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Ingår i: Polymer Degradation and Stability. - : Elsevier BV. - 0141-3910. ; 96:10, s. 1751-1760
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Tidskriftsartikel (refereegranskat)abstract
- Three commercial anti-oxidant systems have been studied regarding migration and chemical reaction in different polyethylene pipe materials during extraction in organic solvents and in hot water, 95-100 degrees C, under anaerobic and aerobic conditions. Materials made of crosslinked and non-crosslinked high density polyethylene, low density polyethylene and blends thereof were stabilized with different phenolic antioxidants: Irganox 1330, Irganox 1010, and Irganox 1076. The loss in stability with increasing extraction times was followed by oxidation induction time (OIT) measurements and by measuring the residual amounts of anti-oxidant by extraction. A gradual decrease in OIT and amount of anti-oxidant with increasing treatment time in water was observed for all samples. However, the behaviour of the three antioxidants was dissimilar. For materials containing Irganox 1330 three new species, possibly transformation products of the anti-oxidant, were found within the material. Larger decrease in antioxidant content in the polymer compared to corresponding loss in OIT indicates that the new species still have anti-oxidant capacity. On the other hand, corresponding transformation species could not be found within materials stabilized with Irganox 1010 or 1076. It is suggested that these antioxidants, which both contain ester groups, are hydrolyzed and that the new species migrate out into the surrounding water. Solvent extractions showed that crosslinking did not affect the extractability of the antioxidants. Actually, even with water as the extracting media, the network did not show any obstructive effect of the migration of the anti-oxidant. For peroxide crosslinked samples part of the antioxidant could not be extracted with solvent but we believe that grafting of antioxidants onto the polymer backbone is the most plausible explanation in this case. Additionally, we see a clear decrease in antioxidant loss with increasing crystallinity.
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